F. S. Dietrich

Bio: F. S. Dietrich is an academic researcher from Lawrence Livermore National Laboratory. The author has contributed to research in topics: Neutron & Nuclear reaction. The author has an hindex of 30, co-authored 124 publications receiving 3234 citations.

Determination of the neutron spin structure function.

Abstract: The authors report the results of the experiment E142 which measured the spin dependent structure function of the neutron, g{sub 1}{sup n}(x, Q{sup 2}). The experiment was carried out at the Stanford Linear Accelerator Center by measuring an asymmetry in the deep inelastic scattering of polarized electrons from a polarized {sup 3}He target, at electron energies from 19 to 26 GeV. The structure function was determined over the kinematic range 0.03 < BJorken x < 0.6 and 1.0 < Q{sup 2} < 5.5 (GeV/c){sup 2}. An evaluation of the integral {integral}{sub 0}{sup 1} g{sub 1}{sup n}(x,Q{sup 2})dx at fixed Q{sup 2} = 2 (GeV/c){sup 2} yields the final result {Lambda}{sub 1}{sup n} = -0.032 {+-} 0.006 (stat.) {+-} 0.009 (syst.). This result, when combined with the integral of the proton spin structure function measured in other experiments, confirms the fundamental Bjorken sum rule with O({alpha}{sub s}{sup 3}) corrections to within one standard deviation. This is a major success for perturbative Quantum Chromodynamics. Some ancillary results include the findings that the Ellis-Jaffe sum rule for the neutron is violated at the 2 {sigma} level, and that the total contribution of the quarks to the helicity of the nucleon is 0.36 {+-}more » 0.10. The strange sea polarization is estimated to be small and negative, {Delta}s = -0.07 {+-} 0.04.« less

Deep inelastic scattering of polarized electrons by polarized 3He and the study of the neutron spin structure.

Abstract: The neutron longitudinal and transverse asymmetries ${A}_{1}^{n}$ and ${A}_{2}^{n}$ have been extracted from deep inelastic scattering of polarized electrons by a polarized $^{3}\mathrm{He}$ target at incident energies of 19.42, 22.66, and 25.51 GeV. The measurement allows for the determination of the neutron spin structure functions ${g}_{1}^{n}(x, {Q}^{2})$ and ${g}_{2}^{n}(x, {Q}^{2})$ over the range $0.03lxl0.6$ at an average ${Q}^{2}$ of 2 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$. The data are used for the evaluation of the Ellis-Jaffe and Bjorken sum rules. The neutron spin structure function ${g}_{1}^{n}(x, {Q}^{2})$ is small and negative within the range of our measurement, yielding an integral $\ensuremath{\int}{0.03}^{0.6}{g}_{1}^{n}(x)\mathrm{dx}=\ensuremath{-}0.028\ifmmode\pm\else\textpm\fi{}0.006 (\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.006 (\mathrm{syst})$. Assuming Regge behavior at low $x$, we extract ${\ensuremath{\Gamma}}_{1}^{n}=\ensuremath{\int}{0}^{1}{g}_{1}^{n}(x)\mathrm{dx}=\ensuremath{-}0.031\ifmmode\pm\else\textpm\fi{}0.006 (\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.009 (\mathrm{syst})$. Combined with previous proton integral results from SLAC experiment E143, we find ${\ensuremath{\Gamma}}_{1}^{p}\ensuremath{-}{\ensuremath{\Gamma}}_{1}^{n}=0.160\ifmmode\pm\else\textpm\fi{}0.015$ in agreement with the Bjorken sum rule prediction ${\ensuremath{\Gamma}}_{1}^{p}\ensuremath{-}{\ensuremath{\Gamma}}_{1}^{n}=0.176\ifmmode\pm\else\textpm\fi{}0.008$ at a ${Q}^{2}$ value of 3 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ evaluated using ${\ensuremath{\alpha}}_{s}=0.32\ifmmode\pm\else\textpm\fi{}0.05$.

Measurements of the electric and magnetic form factors of the proton from Q2=1.75 to 8.83 (GeV/c)2.

Abstract: The proton elastic form factors ${\mathit{G}}_{\mathit{E}\mathit{p}}$(${\mathit{Q}}^{2}$) and ${\mathit{G}}_{\mathit{M}\mathit{p}}$(${\mathit{Q}}^{2}$) have been extracted for ${\mathit{Q}}^{2}$=1.75 to 8.83 (GeV/c${)}^{2}$ via a Rosenbluth separation to ep elastic cross section measurements in the angular range 13\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\le}90\ifmmode^\circ\else\textdegree\fi{}. The ${\mathit{Q}}^{2}$ range covered more than doubles that of the existing data. For ${\mathit{Q}}^{2}$4 (GeV/c${)}^{2}$, where the data overlap with previous measurements, the total uncertainties have been reduced to 14% in ${\mathit{G}}_{\mathit{E}\mathit{p}}$ and 1.5% in ${\mathit{G}}_{\mathit{M}\mathit{p}}$. Results for ${\mathit{G}}_{\mathit{E}\mathit{p}}$(${\mathit{Q}}^{2}$) are consistent with the dipole fit ${\mathit{G}}_{\mathit{D}}$(${\mathit{Q}}^{2}$)=(1+${\mathit{Q}}^{2}$/0.71${)}^{\mathrm{\ensuremath{-}}2}$, while those for ${\mathit{G}}_{\mathit{M}\mathit{p}}$(${\mathit{Q}}^{2}$)/${\mathrm{\ensuremath{\mu}}}_{\mathit{p}}$${\mathit{G}}_{\mathit{D}}$(${\mathit{Q}}^{2}$) decrease smoothly from 1.05 to 0.92. Deviations from form factor scaling are observed up to 20%. The ratio ${\mathit{Q}}^{2}$${\mathit{F}}_{2}$/${\mathit{F}}_{1}$ is observed to approach a constant value for ${\mathit{Q}}^{2}$g3 (GeV/c${)}^{2}$. Comparisons are made to vector meson dominance, dimensional scaling, QCD sum rule, diquark, and constituent quark models, none of which fully characterize all the new data.

Compound-nuclear reaction cross sections from surrogate measurements

Abstract: Nuclear reaction cross sections are important for a variety of applications in the areas of astrophysics, nuclear energy, and national security. When these cross sections cannot be measured directly or predicted reliably, it becomes necessary to develop indirect methods for determining the relevant reaction rates. The surrogate nuclear reactions approach is such an indirect method. First used in the 1970s for estimating ðn; fÞ cross sections, the method has recently been recognized as a potentially powerful tool for a wide range of applications that involve compound-nuclear reactions. The method is expected to become an important focus of inverse-kinematics experiments at rareisotope facilities. The present paper reviews the current status of the surrogate approach. Experimental techniques employed and theoretical descriptions of the reaction mechanisms involved are presented and representative cross section measurements are discussed.

Measurement of neutron total cross sections up to 560 MeV

Abstract: We have completed a new set of total cross section measurements of 31 elements and isotopes spanning the periodic table from A=1 to 238. We employed the same technique as in Finley [Phys. Rev. C 47, 237 (1993)] with refinements intended to allow measurements on separated isotopes and improved systematic error control. The goal of the new measurement was 1% statistical accuracy in 1% energy bins with systematic errors less than 1%. This was achieved for all but the thinnest samples. Stringent checks of systematic errors in this measurement resulted in a reassignment of systematic uncertainties to the neutron total cross sections reported in Finley Microscopic optical model calculations were carried out to interpret the results of the experiment. Two specific types of optical models were employed. The Jeukenne-Lejeune-Mahaux model was used in the range of 5--160 MeV, and a model based on the empirical effective interaction of Kelly was used from 135 to 650 MeV. These models are shown to be useful for predicting both neutron total cross sections and proton reaction cross sections. They are particularly important for light nuclei, for which standard global phenomenological parametrizations of the optical potential are insufficiently accurate.

JENDL-4.0: A New Library for Nuclear Science and Engineering

Abstract: The fourth version of the Japanese Evaluated Nuclear Data Library has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the impro...